1. Field of the Invention
The present invention relates to a ceramic ball and a ceramic ball bearing using the same.
2. Description of Related Art
In general, balls used in ball bearing assemblies (hereinafter referred to as bearing balls) are formed of a metal such as bearing steel. However, in order to improve wear resistance, ball bearing assemblies utilizing ceramic ball bearings have come into wide use. Examples of ceramic used for such ceramic bearing balls include silicon nitride ceramic, alumina ceramic, and zirconia ceramic.
The above-described ceramic balls for ball bearing assemblies are all insulating materials. Therefore, when the ceramic balls in a ball bearing assembly rotate, the ceramic balls are electrified with static electricity generated due to friction. When such electrification occurs excessively during production of balls of small diameter, the balls adhere to an apparatus (e.g., a container), or dust adheres to the balls, thus hindering smooth progress of the production process.
Further, in the case of ceramic balls of a bearing assembly used in a hard disk drive of a computer, if a foreign substance such as dust adheres to the balls, inner ring or outer ring of the bearing due to static electricity, the foreign substance often causes generation of abnormal noise or vibration, because the bearing is used at high speed.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings, wherein like reference numbers refer to the same component, element or feature.
The present invention provides a ceramic ball for a bearing, characterized in that at least a portion of the ball""s constituent ceramic is formed of an electrically conductive inorganic compound phase. Conceptually, the term xe2x80x9celectrically conductive inorganic compound phasexe2x80x9d encompasses a xe2x80x9csemi-conductive inorganic compound phase.xe2x80x9d
The present invention further provides a ball bearing which includes a plurality of the above-described ceramic balls as bearing rolling elements. Such a ball bearing is preferably used as a bearing component of a rotary spindle unit of a hard disk, which is a magnetic storage medium. Specifically, there can be constructed a hard disk drive mechanism which comprises the above-described ball bearing, one of the outer and inner rings of the ball bearing being fixed, and the other of the outer and inner rings serving as a rotary member; a drive unit for rotating the rotary member; and a hard disk which rotates together with the rotary member.
When at least a portion of the constituent ceramic is formed of an electrically conductive inorganic compound phase to thereby impart a proper degree of electrical conductivity to the ceramic, electrification of bearing balls can be prevented or suppressed effectively. This solves the problem involved in production of balls of small diameter such that the balls adhere to an apparatus (e.g., a container), thereby hindering smooth progress of the production process. Further, when the ball is used in precision electronic equipment, such as a hard disk drive for a computer, which is operated at high rotational speed, adhesion of foreign substance to the ball due to electrification and resultant generation of abnormal noise and vibration can be prevented or suppressed effectively. For example, even when the bearing of the present invention is used at high rotational speed (e.g., 5400 to 15,000 rpm) in such precision electronic equipment, long service life can be secured.
Due to the improved electrical conductivity of the ball bearing, in addition to prevention of electrification by static electricity, the following effect is obtained in some cases, depending on the field to which the ball bearing is applied. In a measurement apparatus for semiconductor wafers, such as a measurement apparatus for measuring the flatness of a semiconductor wafer, while a rotary measurement table carrying a wafer is rotated, electricity is applied between the wafer and the rotary measurement table in order to measure an electrostatic capacitance, on the basis of which the flatness of the wafer is evaluated. In such a case, electricity is supplied to the rotary measurement table, typically via a bearing and a rotary spindle of the table, which form a conduction path. Therefore, in order to establish a conduction path between the inner and outer rings of a bearing, bearing balls used in the above-described field have conventionally been formed of a metal such as bearing steel. However, bearing balls formed of a metal is inferior in wear resistance to ceramic bearing balls, so that the metal bearing balls have drawbacks, such as generation of dust and short service life. On the other hand, when bearing balls are formed of an ordinary insulating ceramic, a conduction path cannot be secured.
Thus it is an object of the present invention is to provide a ceramic ball for a bearing which is hardly electrified and thus can prevent occurrence of a problem, such as generation of abnormal noise or vibration, which would otherwise be caused by adhesion of foreign substance, even when the ball is used in a high speed bearing.
A further object of the present invention is to provide a ceramic ball bearing using the ceramic ball.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended claims wherein like reference numbers refer to the same component, element or feature.